1. Field of the Invention
The present invention relates to a balancer and a centrifuge using the same, and more particularly to a balancer which is provided with a curved portion at a balancing space so that movement of balls is accelerated at the moment a rotational speed of a rotor exceeds a resonant speed, thereby stabilizing the rotation of the rotor without vibration regardless of when the rotational speed of the rotor is less or more than the resonant speed, and to a centrifuge using the above balancer to secure the stable rotation of the rotor.
2. Description of the Related Art
Unbalance generally exists at a rotor of a rotating machine, and the unbalance affects adversely a rotational speed, and causes vibration and noise. In order to stabilize unstable rotation of a rotor due to unbalance, a balancer is mounted to the rotor.
Especially, a high-speed rotor, e.g., used in a centrifuge has relatively large unbalance. In such a high-speed rotor, a ball balancer is used for preventing reduction of a rotational speed and generation of vibration and noise due to the unbalance.
FIGS. 18 and 19 illustrate examples of a conventional ball balancer.
A ball balancer illustrated in FIG. 18 includes a casing 10 which has a balancing space 30 of an annular shape, and a plurality of balls 20 which are provided in the balancing space 30. The casing 10 is formed with a shaft hole 40 at its center portion, through which a rotating shaft is fixedly coupled.
In the conventional ball balancer structured as above, the number of the balls 20 is provided to an extent of occupying a portion of the balancing space 30. When a rotational speed of a rotor is higher than a resonant speed, the balls 20 are moved to an opposite direction to an unbalance position, thereby balancing the rotor and stabilizing the rotation. However, when the rotational speed of the rotor is lower than the resonant speed, the balls 20 are moved to the unbalance position, thereby further destabilizing the rotation of the rotor.
In order to solve the above problem, another conventional ball balancer structured as illustrated in FIG. 19 has been developed.
The conventional ball balancer illustrated in FIG. 19 includes a hollow casing 10a, and a plurality of balls 20a provided in a balancing space 30a which is defined by an inner surface of the casing 10a such that the inner bottom surface of the casing 10a is slanted downward from a center portion to a circumference. The number of the balls 20a are provided to an extent of filling a recess of the balancing space 30a formed along the inner circumference of the casing 10a. A non-described reference numeral 40a is a shaft hole formed at the center portion of the casing 10a, through which a rotating shaft is fixedly coupled.
In the conventional ball balancer structured as above, when a rotational speed of a rotor is lower than a resonant speed, the balls 20a are located equidistantly from the center of rotation. Accordingly, the unstable rotation caused by the ball balancer in FIG. 18 at the low rotational speed can be prevented.
Also, when the rotor is rotated at a high speed, the balls 20a take off and are moved to an opposite direction to an unbalance position, thereby stabilizing the rotation of the rotor, and decreasing vibration and noise.
However, the conventional ball balancer in FIG. 19 has a shortcoming that it takes much time for the balls 20a to move to the opposite direction to the unbalance position when the rotational speed of the rotor is increased to exceed the resonant speed, and vibration is generated at this moment. Therefore, the conventional ball balancer does not have a sufficient vibration damping effect.
The aforesaid balancer is used in a high-speed rotating machine like a centrifuge. A centrifuge is a machine that spins mixtures of different substances around very quickly so that they separate by a centrifugal force. As shown in FIG. 20, a centrifuge includes an outer case 700, a damper 200 which is mounted to a supporting plate 701 formed at an inner surface of the outer case 700, a motor 300 which is mounted to a bracket 302 supported elastically by the damper 200, and a rotor 400 which is mounted to a rotating shaft 301 of the motor 300. The rotor 400 is formed with a plurality of chambers, in which bottles or test tubes containing samples to be centrifuged are disposed.
In the centrifuge structured as above, by the motor 300 being driven at high speed, a centrifugal force is exerted to the samples in the bottles or the test tubes which are disposed in the chambers, so that substances contained in the sample separate by the centrifugal force due to a difference of density.
In order to apply the strong centrifugal force to the samples, the motor 300 and the rotor 400 must be rotated at high speed. And, for smooth operation of the centrifuge, vibration should not be generated.
However, the rotor generally has unbalance, and the unbalance affects adversely a rotational speed of the rotor and causes vibration. The unbalanced rotation of the rotor deteriorates a centrifuging effect. When the rotational speed of the rotor of the centrifuge is more than a resonant speed, the substances contained in the sample separate by a difference of density. Then, by decreasing the rotational speed gradually, the separated substances are prevented from being remixed. However, if vibration is generated at the rotor in the above centrifuging process, the separated substances are remixed.
Therefore, it is important to continuously prevent the generation of vibration while the rotational speed of the rotor is increased or decreased. But, the conventional centrifuge has a drawback that vibration is generated at the moment the rotational speed of the rotor is decreased below the resonant speed and the separated substances are remixed. Although the conventional centrifuge includes the damper to solve the vibration problem, the damper cannot absorb the vibration sufficiently.